Summernats, an annual car event that has been held in Canberra every year since 1987, is expected to have as many as 100,000 people attended over the four days, with almost 2000 entrants registered for 2018.

With temperatures predict to soar into the mid 30s, Weatherzone meteorologist Brett Dutschke urged festival goers to be sun safe.

"It's looking like it will get progressively hotter, but the start of the festival looks reasonably comfortable weather," Mr Dutschke said.

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"It'll be in the high 20s on Thursday with plenty of sunshine, so it'll be sunnier and warmer than Wednesday and not too windy.

Mr Dutschke said it would be a pleasant few days, but come Friday and temperatures would be in the low 30s with lost of sunshine.

"People will start to feel the heat on Friday, and on Saturday and Sunday it's looking to be very similar in terms of temperatures between 36 to 37 degrees," he said.

"I think while a lot of people will be travelling from far, for locals this will be a night that could be difficult to sleep on because on Saturday night, after about a 36 to 37 degree day, it's still likely to be near 30 degrees at about eight o'clock at night and about 24 degrees at midnight."

He said Sunday would be cooler in the evenings, with a small chance of showers would bring a cool relief after a few hot days.

"There's a risk of people getting heat stroke if they're outside all day and in the sunshine," he said.

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"It's good to advise people to dress sensibly, hats and long sleeves and that sort of thing.